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A voltammetric sensor comprising a paste electrode made of graphitized thermal carbon black CarboblackC and nanosized zeolite MFI was developed for selective recognition and determination of tryptophan enantiomers. It was found that in determining tryptophan enantiomers, the dependence remains linear at concentrations from 5×10−5 to 1×10−3 M. The detection limits of tryptophan L‐ and D‐enantiomers were calculated to be 4.98×10−7 M and 3.20×10−7 M, while their lower limits of determinable concentrations–1.66×10−6 M and 1.07×10−6 M, respectively. The sensor is more sensitive to D‐tryptophan (ΔEp=20 mV, ipD/ipL=1.58). The developed sensor was shown to successfully determine tryptophan enantiomers in model solutions of pure enantiomers, in a mixture of enantiomers, in biological fluids, and in tablet forms of biologically active additives. It was shown that the suggested sensor made it possible to determine the ratio of L‐ and D‐enantiomers of tryptophan in a mixture with a high probability. [ABSTRACT FROM AUTHOR]

The use of chiral modifiers is among the simplest and most popular strategies for synthesizing enantioselective voltammetric sensors that are applied for the analysis and discrimination of enantiomerical drugs in various media. The type and structure of the chiral modifier are the key factors for the creation of enantioselectivity to a specified analyte. We suggest a novel approach to the prediction of the quality of a chiral modifier for preparing highly enantioselective sensors. The suggested approach is based on the molecular mechanics modeling of the adsorption of analyte enantiomers on chiral modifiers and on the comparison of the corresponding adsorption energies (ΔEads). The efficiency of our approach is demonstrated using the example of cyclodextrins and chiral single‐wall carbon nanotubes as chiral modifiers, and a wide range of chiral analytes. We found that the experimental enantioselectivity (ϑexp) measured using voltammetry linearly correlates with ΔEads. The suggested approach also showed good predictive power in application to enantioselective chromatography, which further validates its general applicability. [ABSTRACT FROM AUTHOR]

In this work, we study the structure and ratio of (R)‐4‐menthen‐3‐one conformers using ab initio methods. It was shown that the methyl group in (R)‐4‐menthen‐3‐one preferred an equatorial position. In the most stable conformer of the (R)‐4‐menthen‐3‐one, the methyl radical of the i‐Pr group is oriented to C=C double bond, so this group has a more steric hindrance effect on double bond. The ratio of conformers in solvents increases in favor of the most stable conformer. [ABSTRACT FROM AUTHOR]

Lewis acid–base complexes AlMe3-YH3 (Y = N, P, As) and their components have been investigated by means of quantum chemical techniques at the RHF, MP2, MP4, and DFT (PBE0) levels of theory, using the cc-pVDZ and cc-pVTZ basis sets. Theoretical complex formation energy for the AlMe3-YH3 complexes increases in the order NH3 ≪ PH3 < AsH3 for all investigated complexes. Distortion of AlMe3 from planarity under complex formation leads to decreasing C&bond;Al&bond;C angles along with increasing Al&bond;C bond length. For all investigated adducts, an inverse negative relationship correlation between Y&bond;Al&bond;C valence angle and Al&bond;Y bond length has been found. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]